Integrated oscillator circuits

Abstract: A stable sine wave oscillator circuit comprising two pairs of cross-coupled bipolar transistors in cascode, the collector electrodes of the transistors of each pair being interconnected by way of respective capacitors. Output signals in phase quadrature may be obtained from across these two capacitors.

Description: The present invention relates to oscillator circuits suitable for inclusion in integrated circuits. In particular the invention is concerned with oscillator circuits for providing stable sine-wave outputs. Oscillator circuits are known, for example from United States Patent US 3983512, in which the resonant or frequency selective circuits are constructed utilising capacitors and cross-coupled transistor pairs, the frequency of oscillation or resonance being dependent upon the emitter resistances of the transistors, which may be controlled by controlling their d.c. emitter currents. In the arrangements disclosed in this U.S. Patent, however, a separate amplifier is required to provide the gain to sustain oscillations. According to the present invention a stable sine-wave oscillator circuit comprises a first bipolar transistor having its emitter electrode connected to one terminal of a current source and its collector electrode connected to the emitter electrode of a second bipolar transistor the collector electrode of which is connected to a first supply voltage conductor by way of first load means, a third bipolar transistor having its emitter electrode connected to said one terminal of said current source and its collector electrode connected to the emitter electrode of a fourth bipolar transistor the collector electrode of which is connected to said first supply voltage conductor by way of second load means, the other terminal of said current source being connected to a second supply voltage conductor, a first capacitor connected between the collector electrodes of said second and fourth transistors and a second capacitor connected between the collector electrodes of said first and third transistors, the base and collector electrodes of said second and fourth transistors being cross-connected and the base and collector electrodes of the first and third transistors being cross-connected. The first and second load means may comprise respective load resistors or respective diodes, or may comprise emitter/collector paths of further bipolar transistors in series with respective load resistors, the base electrodes of said further transistors being connected to said first supply voltage conductor. Oscillator circuits in accordance with the present invention will now be described with reference to the accompanying drawings, of which:- Figures 1 to 3 show diagrammatically respective different embodiments of the invention. Referring first to Figure 1 the basic oscillator circuit in accordance with the present invention comprises four bipolar npn junction transistors 1 to 4 which are connected in two cross-connected cascoded pairs. The emitter/collector paths of transistors 1 and 2 are connected in series with a load resistor 5 between a supply conductor 17 and one terminal of a curent source 9 the other terminal of which is connected to a supply conductor 18. The emitter/collector paths of transistors 3 and 4 are connected in series with a load resistor 6 between the supply conductor 17 and the one terminal of the current source 9. The collector electrodes of the transistors 2 and 4 are interconnected by way of a capacitor 7, and the base and collector electrodes of these transistors are cross-connected. Likewise the collector electrodes of the transistors 1 and 3 are interconnected by way of a capacitor 8 and the base and collector electrodes of these transistors are cross-connected. Differential outputs 10 and 11 are taken from the collector electrodes of the transistors 2 and 4 and 1 and 3 respectively. By virtue of the charging and discharging currents flowing in operation to the capacitors 7 and 8 the oscillatory signals at the outputs 10 and 11 are in phase quadrature. The circuit oscillates at a frequency which is proportional to the value of current provided by the current source 9 and which is inversely proportional to the values of the capacitors 7 and 8. The load resistors 5 and 6 may be replaced by diodes 12 and 13 as shown in Figure 2, or diode-connected transistors 14 and 15 respectively may be connected between the collector electrodes of the transistors 2 and 4 and the load resistors 5 and 6, as shown in Figure 3. In the latter arrangement a third output 16 may be taken between the collector electrodes of the transistors 14 and 15, signals at this third output being in phase with signals at the output 10. The circuit is capable of a very wide tuning range, by adjusting the current value provided by the current source 9, and is ideally suited to performing the local oscillator function in superheterodyne, homodyne and image cancelling radio receivers. Of particular advantage is the use of a single current source, resulting in minimum power consumption.

Claims: A stable sine-wave oscillator circuit comprising a first bipolar transistor (1) having its emitter electrode connected to one terminal of a current source (9) and its collector electrode connected to the emitter electrode of a second bipolar transistor (2) the collector electrode of which is connected to a first supply voltage conductor (17) by way of first load means (5, 14, 12), a third bipolar transistor (3) having its emitter electrode connected to said one terminal of said current source (9) and its collector electrode connected to the emitter electrode of a fourth bipolar transistor (4) the collector electrode of which is connected to said first supply voltage conductor (17) by way of second load means (6, 15, 13), the other terminal of said current source (9) being connected to a second supply voltage conductor (18), a first capacitor (7) connected between the collector electrodes of said second and fourth transistors (2, 4) and a second capacitor (8) connected between the collector electrodes of said first and third transistors (1, 3), the base and collector electrodes of said second and fourth transistors (2, 4) being cross-connected and the base and collector electrodes of the first and third transistors (1, 3) being cross-connected. An oscillator cicuit in accordance with Claim 1 wherein said first and second load means comprise respective load resistors (5, 6). An oscillator circuit in accordance with Claim 1 wherein said first and second load means comprise respective respective diodes (12, 13). An oscillator circuit in accordance with Claim 1 wherein said first and second load means comprise respective emitter/collector paths of respective further bipolar transistors (14, 15) in series with respective load resistors (5, 6), the base electrodes of said further transistors (14, 15) being connected to said first supply voltage conductor (17). An oscillator circuit in accordance with any one of Claims 1 to 3 wherein the collector electrodes of the second and fourth transistors (2, 4) are connected to a first pair of output terminals (10) and the collector electrodes of the first and third transistors (1, 3) are connected to a second pair of output terminals (11). An oscillator circuit in accordance with Claim 4 wherein the collector electrodes of said second and fourth transistors (2, 4) are connected to a first pair of output terminals (10), the collector electrodes of said first and third transistors are connected to a second pair of output terminals (11), and the collector electrodes of said further transistors (14, 15) are connected to a third pair of output terminals (16).

Inventors: LAWTON RODNEY JAMES, LAWTON, RODNEY JAMES
Applicants: MITEL SEMICONDUCTOR LTD, MITEL SEMICONDUCTOR LIMITED
Application year: 1994
Main classification: H03B5
IPC codes: H03B5, H03B27, H03K3